An inflator for inflating an inflatable vehicle occupant protection device, such as an air bag, contains an ignitable gas generating composition. The inflator includes an igniter. The igniter is actuated so as to ignite the gas generating composition when the vehicle experiences a collision for which inflation of the air bag is desired to help protect a vehicle occupant. As the gas generating composition burns, it generates a volume of inflation gas. The inflation gas is directed into the air bag to inflate the air bag. When the air bag is inflated, it expands into the vehicle occupant compartment and helps to protect the vehicle occupant.
A gas generating composition that uses particulate ammonium nitrate as an oxidizer source has the advantage that it produces upon combustion high gas outputs and low levels of residual solids. Particulate ammonium nitrate agglomerates, however, and forms clumps that must be mechanically broken prior to using the particulate ammonium nitrate in a gas generating composition. A typical method of mechanically breaking the clumps of ammonium nitrate is by grinding the clumps of ammonium nitrate in a ball mill. Ammonium nitrate is hygroscopic and can potentially absorb moisture from the air during the grinding process. The absorbed moisture can potentially render the particulate ammonium nitrate unsuitable for use in a gas generating composition for inflating an inflatable vehicle occupant protection device.